1. Field of the Invention
This invention relates to the depositing of metal onto a surface of a metal article. Specifically, the invention is directed to the detection of an incipient change of phase from solid to liquid by means of a light beam in combination with a detector which is sensitive to the reflected light and which can distinguish the difference in reflections from a solid and a plastic body. The detection produces a control signal when incipient fusion is achieved, and the control signal is used to control deposit of metal on the surface.
2. Description of the Prior Art
Typical prior methods and apparatuses for depositing metal on a metal article have relied upon the attainment of a particular temperature in the workpiece as an indication of the appropriate time for applying the metal material, or reliance was placed upon the visual judgment of the operator. In such prior art methods and apparatuses, the workpiece is heated until the surface becomes molten and visually appears to be "wet" and when the surface is judged to be uniformly "wet", the metal material is applied. Due to variations in the composition of the material of the workpiece, melting temperature can fluctuate, and thus temperature measurement alone is not a reliable technique for determining surface melting. Further, relying on the judgment of the operator is not a efficient or reliable as automatic control.